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Professional's Knowledge Network
pap-RAWCX Analysis Of The Failure Of A Chiller Tube In An Industrial Boiler J.C.Guild
The investigation into the failure of a boiler chiller tube is described. The failure was by way of longitudinal bursting of the tube. It was ascribed to excessive temperatures being reached, and it is recommended that the boiler be modified in such a way that these tubes are no longer required

pap-VZVWR Analysis Of The Failure Of A Synthesis Gas Rotor Coupling And Turbine Shaft J.C.Guild
The investigation into the failure of a synthesis gas rotor coupling and turbine shaft is described. The failure was by way of corrosion fatigue, originating at corrosion pits on the inside surface of the coupling.

pap-FOSEP Analysis Of The Failure Of A T Joint Between A Process Pipeline And A Relief Valve Pipeline J.C.Guild
The investigation into the failure of a T joint where a relief valve line was joined into a process line is described. Due to the service of the line, a number of different degradation mechanisms were possible. These had to be investigated before the final conclusion as to the failure mode could be reached. Recommendations to prevent future failures are given.

pap-XZDTM Closed-Loop Vibration Control Experiments On A Rotor With Blade Mounted Actuation Eric Prechtl, Steven Hall
A Mach-scaled CH-47 model rotor blade with an actively controlled servo-flap near the tip was designed, manufactured, and tested. The servo- flap was powered by an “X-Frame" piezoelectric actuator. Using hover test data, the transfer function of the rotor (from servo-flap deflection to vertical hub shear) was determined. The servo- flap produces significant control authority, especially near the 3/rev frequency that would be important for the CH-47. Closed-loop feedback control was experimentally applied to the model rotor system. Both single frequency and combined frequency controllers were implemented on the rotor, and produced significant reduction in the vibration level. Most significantly, simultaneous control of 1/rev, 3/rev, 4/rev, 5/rev, and 6/rev harmonic vibration was successfully demonstrated. The peak vibrations were eliminated at each frequency, as well as the vibrations over a small bandwidth surrounding each peak. Comparison of continuous-time and discrete-time controllers was made. Continuous-time controllers were shown to produce more effective vibration reduction.

pap-IVZAF Design And Manufacture Of An Integral Twist-Actuated Rotor Blade * John P. Rodgers, Nesbitt W. Hagood, Douglas B. Weems
The objective of this research is to develop an actuated blade for use in the control of rotor vibrations. Active fiber composites are integrated with the composite spar to induce shear stresses within the spar laminate and thus a distributed twisting moment along the blade. This paper details the design of an active blade model based on a 1/6th Mach scale Chinook CH-47D. The design goals are ±2° of blade tip twist with a maximum of 20% added blade mass. The fabrication of a model blade section is included in the paper as well as preliminary structural and actuation testing.

pap-YCGHJ Design Of A High Effciency, Large Stroke, Electromechanical Actuator Eric Prechtl, Steven Hall
Large stroke, electromechanical actuator designs are considered. Special emphasis is placed on actuators designed to power a trailing edge servo-flap system for feedback control of helicopter rotor vibration, acoustics, and aerodynamic performance. A survey was conducted comparing the advantages and disadvantages of a number of actuator designs. The major conclusions from this survey indicate that any successful actuator design will utilize a high bandwidth active material, produce large amplification of the active material stroke, and incorporate a simple compressive pre-stress mechanism, while remaining efficient in a mass normalized sense. The mass efficiency, defined as the ratio of the specific work performed by the actuator to the specific energy available in the active material element, was used as a metric to rate the actuators considered in the survey. This metric is appropriate in aerospace applications where weight is critical. The most feasible discrete actuators are those where the active material reacts against an inert support frame housing. An upper bound on the mass efficiency of this type of actuator is shown to be a function of the ratio of active material to frame specific modulus. A new high efficiency discrete actuator, the X-Frame Actuator, is described. A prototype of this actuator was built and tested to confirm the predicted performance. The prototype demonstrates an output energy density of 14.6 ft-lb/slug. It has a bandwidth of about 540 Hz when driving a nearly impedance matched load.

pap-SYDMJ Design, Manufacture, And Testing Of An Integral Twist-Actuated Rotor Blade John P. Rodgers, Nesbitt W. Hagood
An active blade designed for the control of rotor vibrations and noise has been developed. Active fiber composites have been integrated with the composite spar to induce shear stresses within the spar laminate and thus a distributed twisting moment along the blade. The design of an active blade model based on a 1/6th Mach-scale Chinook CH-47D is reviewed. The design goals included ±2° of blade tip twist with a maximum of 20% added blade mass. The fabrication of the actuators and a model blade section are described. Next, results from benchtop testing of the blade section including stiffness, twist actuation, and survivability under tensile load are presented. Results are compared with model predictions and design improvements are suggested for the complete blade.

pap-FMLNG Hover Testing Of A 1/6thmach-Scale Ch-47d Blade With Integral Twist Actuation John P. Rodgers, Nesbitt W. Hagood
An integral twist-actuated rotor blade has been developed for helicopter Individual Blade Control (IBC) applications. A 1/6th Mach scale CH-47D blade was designed, fabricated, and tested in hover at the MIT Hover Test Stand Facility. The design incorporates Active Fiber Composite (AFC) actuators within the composite spar to induce a distributed twisting moment along the span. The anisotropic actuators are oriented at 45° to the blade axis to maximize the shear stresses generated. The twist actuation performance of the active blade was evaluated over a range of rotor speeds, actuation frequencies, and blade loading conditions in hover. Transfer function data were collected from input voltage to blade twist and induced vertical hub shear. Changing test conditions had little affect on the measured performance, though blade flapping mode dynamics had a significant effect. This project successfully demonstrated the effectiveness of integral twist actuation in Mach-scale hover testing, supporting the need for further investigation of the concept for IBC

pap-JJQKA Investigation Into The Failure Of A 16 Inch Pipe Bend In A Nox Gas Pipeline At A Nitric Acid Plant J.C.Guild
The investigation into the failure of a Titanium stabilized (Type 321) stainless steel pipe bend, in NOX gas service, is described. A metallurgical examination revealed that the materials used appear to be acceptable to the relevant specifications, but that the failure was due to “knife-line” corrosion adjacent to the welds. This occurred due to the presence of condensed Nitric / Nitrous acid in the line. Recommendations are made to monitor the rest of the line.

pap-SJSGN Investigation Into The Failure Of A Gas Washing Fan On An Ammonia Plant J.C.Guild
The investigation into the failure of a washing fan impeller, which lead to a fatality, is described. A number of mechanisms were involved in the failure, including corrosion fatigue, hydrogen imbrittlement and brittle failure. The brittle failure was as a result of the martensitic stainless steel’s heat treatment being incorrect.

pap-PWPGL Investigation Into The Failure Of A Weld In ½ Mo Steel Piping In Carbon Monoxide Conversion J.C.Guild
The investigation into the failure of a ½ Mo steel pipeline in carbon monoxide conversion service is described. A previous failure was attributed to creep damage, but the present failure is attributed to hydrogen damage. Both failures occurred in weld repairs. Recommendations are given to assess plant condition and prevent future failures.

pap-HGFEF Preliminary Testing Of A Mach-Scaled Active Rotor Blade With A Trailing Edge Servo-Flap Eric Prechtl, Steven Hall
The results of preliminary tests on an active helicopter rotor blade are presented. The blade, a Mach-scaled model of a CH-47D helicopter blade, has a discrete piezoelectric actuator embedded within the spar that controls a trailing edge flap via a pushrod. Ultimately, the blade will be tested on a helicopter rotor hover stand at MIT. In this paper, we describe the tests performed prior to hover testing. First, the actuator was tested on the bench to determine its control authority and frequency response. Second, the actuator was tested on a shake table to simulate the out-of-plane accelerations that would be encountered in a full-scale helicopter in forward flight. Third, the actuator was embedded in the model blade, and its response to low-frequency sinusoidal actuation was obtained and compared to the bench test results. Finally, the frequency response of the actuator in the blade was determined using swept sine excitation. All test results indicate that the actuator should produce the desired level of control authority in the model-scale rotor

pap-MYZBW Professionals in the Knowledge Economy N.J.Jooste
The knowledge economy is resulting in a changing landscape for professionals. This is especially so regarding their ability to maintain a high output while still keeping up to date with the changes in their particular field of expertise. This difficulty is the result of an information overload. But what is this knowledge economy, and where has it come from? More importantly, where is it going? These questions are addressed, as well as issues surrounding marketing strategies in the “pull” market that is busy expanding globally. While the article does not attempt to predict the future, it may help professionals to better understand some of the important issues for the future and therefore assist professionals in making more informed decisions in this regard

pap-SJQOD Remaining Life Analysis For A Pressure Vessel Subjected To Cyclic Loads Based On Fracture Mechanics G. Duvenhage, J. Wannenburg
Fracture mechanics has evolved into an engineering tool able to solve problems related to the safety of structures containing defects. In practice, however, a wide choice of parallel methods as well as unsolved discrepancies in the theory requires engineering judgment and pragmatism. In this paper a practical case study is presented, concerning a maintenance strategy assessment performed on a welded pressure vessel. The pressure vessel is analyzed in terms of leak-before-break arguments, proof test logic, fatigue initiation life, defect initiation and unstable growth critical sizes, fatigue crack propagation that leads to fracture or leakage, as well as probabilistic methods based on defect size distributions and NDE detection probabilities. The paper deals with some background to the theories employed, the different steps of the assessment methodology, as well as with the interpretation of the result to design a practical and safe maintenance strategy.

pap-QTWSD The Effect Of A Long Post Weld Heat Treatment On The Integrity Of A Welded Joint In A Pressure Vessel Steel C. Smith, P. G. H. Pistorius, J. Wannenburg
The effect of a long post weld heat treatment on the microstructure and mechanical properties of a welded joint in a 0.2%C – 1.4%Mn – 0.5%Mo pressure vessel steel was studied. Multipass submerged-arc welds were made at a heat input of 1.2 and 4.3 kJ mm-1. Individual microstructural regions observed in the heat-affected zone of the actual weld were simulated. These regions were brittle in the as-simulated condition. Post weld heat treatment for periods of up to 40 h at 620 C resulted in a significant improvement in the Charpy impact toughness. At the same time, a loss of the heat-affected zone and weld metal hardness and transverse weld strength occurred. A fracture toughness (JIC) of 134 kJm -2 was measured in the heat-affected zone of the 4.3 kJ mm-1 welds after prolonged post weld heat treatment. The improvement in weldment toughness with post weld heat treatment was primarily attributed to softening of the structure.

pap-CLTAG The Interpretation Of Fracture Toughness Data Johann Wannenburg
The rising importance of accurate fracture mechanics analyses for life extension purposes has placed larger responsibilities on the analyst to ensure accurate analysis inputs. Often, the most costly and confusing part of this process is to establish the fracture toughness data. This paper presents a summary of the different experimental methods that is used and puts into perspective the interpretation of such results in terms of the global objectives and restraints. It is shown that the standard methods for determining linear elastic, as well as elastic-plastic fracture toughness parameters are largely outdated and should be replaced with a single, unambiguous method.

pap-TLTCB The Use Of Probability Theory In Fracture Mechanics – A Case Study J. Wannenburg, G.C. Klintworth, A. D. Raath
A probabilistic approach to fracture mechanics in the form of a typical case study is described wherein the integrity of a high-pressure, water pipeline is assessed. An analysis methodology is discussed incorporating the probability density functions of defect sizes, the statistics of defect occurrences and the statistical distribution of material properties. This method enables the analyst to supply a very simple assessment of safety, based on the probability of failure, (a single number) which may be compared to accepted industrial standards. (e.g. 10-6 for nuclear applications) It is argued that this method often offers the only way to scientifically and economically assess the integrity of fracture prone structures.